Adaptive Multirate Wide Band (AMR-WB) is a speech-compression algorithm that offers substantially superior voice quality (even in noisy environment) because of doubled throughput, without extra radio and transmission bandwidth requirements.
It is standardized in 3GPP Rel-5 and applicable in 3GPP mobile circuit switched systems (e.g., GSM, WCDMA), as well as packet switched systems (e.g., IMS Telephony, VoIP).
AMR-WB has nine coding rates, including the first three rates 6.60, 8.85, and 12.65 kbps, which constitute the mandatory multi-rate configuration.
The ongoing evolution of wireless communication systems and mobile phones has given rise to a variety of compelling mobile applications (e.g., music player, camera, game console) and services (e.g., mobile internet, mobile TV, etc.). Likewise, many services have evolved significantly in order to satisfy user demands. In contrast, from a user perspective, voice telephony has not changed noticeably since mobile telephony was still very new. Notwithstanding, voice service has continued to evolve. Significant milestones include the introduction of the enhanced full-rate codec (EFR) and, later, the Adaptive Multirate (AMR) voice codec, which increased voice quality and boosted channel error robustness and capacity. The narrowband AMR (AMR-NB) codec, which supports the bandwidth of traditional telephony, is now widely deployed in GSM/EDGE and UMTS systems. It is also the codec of choice for the forthcoming multimedia telephony service for IMS (MTSI) standard from 3GPP.
The new wideband AMR (AMR-WB) codec, whose voice frequency band is twice that of AMR-NB, enables telephony services with true, natural voice quality, clearly outperforming other existing mass-market telephony services, including those used for wire-line telephony.
However, a phenomenon exists when, for instance, a caller changes between cells. When an AMR-WB call is transferred into an AMR-NB call, an audible degradation in voice sound quality results.
The principle for bandwidth extension presently used is illustrated in FIG. 1. An incoming AMR NB call 5 to the device is processed to generate a high frequency element in a non-linear element 6 and then filtered using a multi-tap FIR (Finite Impulse Response) filter 7 for overtone shaping, which is added 8 to the incoming AMR-NB call to produce a call with fixed bandwidth and bandwidth extension. The result 9 is a call with extension added fixed bandwidth.